Zeroizing means for dial indicators



. July 1949- A. H. EMERY 2,476,713

zmnoxzme MEANS FOR DIAL INDICATORS Filed April 24, 1945 I iEI.E.

' INVENTOR ALFRED H. EMERY I I ATTORNEYS Patented July 19, 1949 TENT; emu; 1

Alfred Hamilton Emery, Wappingers Falls, N. Y., assignor to Standard Gage Company, Inc.,-

' Poughkeepsie, Y., a corporation of New York p Application April 24, 1945, Serial No. 589,982: ,1.

,2 Claims. (01. 33-172) The present invention relates to a dial gage and particularly to a means for adjusting the position of the gear train of such a sage so that over its normal range of operation the gage will yield accurate readings.

In the past it has been common practice in inspecting and testing dial gages for precision measurement of the typesuch as is here disclosed to check the gages by utilization of Johansson or Hoke blocks and if it was found that over the useful range of measurement the gage wasnot accurate to assume that this inaccuracy resulted from slight inaccuracies in the gear train and to overcome the condition by disassembling the gage and rotating one of the gears through a tooth space to thereby place different teeth in contact and eliminate the error. In some instances as much as eight hours have been spent on a single gage by this trial and error method before the gage was caused to register accurately;

My present invention provides a means of adjustment between the'measuring plunger of the indicator and the gear train thereof to thereby place different gear: and rack teeth in contact through the useful measuring range of the instrument and thus provide a means by which final adjustment can be achieved without disassembling the instrument.

It is an object of my invention to provide a means for adjusting the position of the measuring plunger of a dial indicator with respect to the elements of the gear train of such an indicator to thereby provide a means of adjusting the indicator to give accurate readings throughout its useful range. j

It is a further object of my invention to provide such an adjusting means which is simple and economical of manufacture and is conveniently and easily adjusted'by'means of common tools and without the need for skilled labor.

Other objects and features of my invention will be apparent when the followin description is read in connection with the accompanying drawings in which- Figure 1 is a front elevational view of a dial indicator illustrating the type of indicator to which my invention may be applied;

Figure 2 is a rear elevational view of the indicator of Figure 1, the cover being broken away to illustrate the interior mechanism and particularly the adjustment means of the present invention;

Figure 3 is an enlarged detail view of a portion of the structure of Figure 2 illustrating particularly the adjustment means with respect to the ease with which such'means may be operated;

Figure 4 is an enlarged detail view of the same parts as is shown in Figurea the viewbeing taken, however, at right angles to that of Figure 3 and showin particularly th manner in which the adjustment means alters the relation between the measuring plunger of the gage andthe rack which is the first element of the gear trainy Figure 5 is a cross-sectionalviewtaken on the plane of the line 55 of Figure 3 and showing the adjustment means; and a Y Figure 6 is a fragmentary view of meshing teeth of two gears of the gear train illustrating the necessity for adjustment to avoid imperfect teeth being in action duringmeasurements over the useful range of the instrument.

Referring now to the drawings there is shown in Figure l a dial indicatorQ'gage comprising the usual body portion I 0,'dial ll, pointer l2, housing extension I3, measuring plunger l4 and contact button l5. This dial indicator gage is of the shockproof type as disclosed'in Emery Patent No. 2,178,745, issued on November7, 1939. l

As seen in Figure 2 theindicator ism'ade shockproof by virtue of the rack l6, being slidably mounted on the measuring plunger il l and being urged in a measuring'direction' by thespring l! and being permitted to move ina measuring direction only when thepin l8 fastenedtoplunger l4 moves upwardly in a groove in guide block I9.

In adjusting a gage it 'is'es'sential that over a portion of its range all, readings be'exactJ For example, in such a gage as that shown in Figure 1, final testing would be performed by utilizing Johansson blocks. For exampleja block 1" in thickness would be placed "onth'e anvil of a comparator and the gage adjusteduntil the pointer was exactly on the zero'division'. Thereafter, a block or stack of blocks measuring 1.001" would be substituted for the 1" block and the hand of the gage should then rest on the +.001 graduation. If it does so lie the 1.001" stack of blocks is removed from the comparator and a stack of blocks of 0.999" is substituted. At this time the gage hand should rest on the .001 graduation and, of course, if it does the gage is accurate within the commonly used range of measurement thereof and is deemed to be correct.

However, it not infrequently occurs that due to irregularities in the contours of the teeth of the gears or the rack of the instrument, the gage will not give the proper reading at either the upper or the lower limit or both. The teeth of these gears are of involute form and are very small and consequently very difficult to produce. Any slight inaccuracy in the contours of the gear teeth such, for example, as the elevation shown at 20 in Figure 6, will produce an erroneous reading and in the past the only way of adjusting the gage to eliminate this condition was to disassemble the gage and rotate the ofiending gear, or move the rack-or otherwise alter therelationshipbetwee n the gear teethin such manner that the imperfect tooth would not be in contact with another tooth during the movement 'of the hand over the useful rangea's abevedescribed. Thus if upon inserting thestack of blocks measuring 1.001" in the example "above given, the hand did not come to the 1 graduation, the gage was disassembled "and a gear rotated through a few tooth spaces and then' reassembled and the test made again. Of course, if the test was this time successful the following "test with the stack of blocks of .999" was made, while if the test was-unsuecessfui t'hegage was then disassembled and reas'serrihled unt-i1 success was achieved. In the same manner the test with the .999 stack of-hlocks "-wasrepeated until the "gage gave a reading o'f lflbl.

By my preserit invention 1 have "eliminated all of this disassembling and reassemhling of the gage. This has -*bee'n accomplished "by substituting for the usual "round "pinj'which pin co operates with pin td-to limit the motionof "the rack with respect "tof'theplunger;ainec'ceritric'pin 2| (see Figure 4) whidh likewise'c'o'operates with the pin 18 but renders the i=relations'hip of "the limit of movement of the rack "withresp'eefto the plunger adjustable;

Referring 'now*'to'Tigures '3, 4 and 5,there shown therein in enlarged rdetail the eccentric pin '21 which pinf'GUll'l'PliSS the two co :axiai end portions '22 and "2-3"and"the"eccentric centralfportion 24, the pin being "provided "with a slotted head 25. This pin, 21 extends acrws the slot '26 inthe "rack member I 6 and cooperates with "the pin [8 which, as has beenstated, "is 'fiXBdiinIin-d extends from "the plunger 1.4. Thus'by rotating the pin 2: *theposition'ofthe rack'with'res ect to the plunger may be valtered "and clearly .such alteration will aifect thefgear train so'that different teeth willbein contactattheitime whenthe hand reads at 'eitheroffits limits as WILas atiits zero point. Therefora'itis'orilynecessary,after testing to'find *whetherfor not the hand moves properly to the X101 graduation .w'henlthe stack of blocks of 11091 dimension 'is'inithe comparator, to slightly rotate the eceentriclpin'fl mesa-mash this relationship if it idoesl not exist, thereby .oo 1.- pletely eliminating "the necessity for disassembling and reassembling "the gage. Of course,

after the upper limit llrasbeemproperly set, atest for the :lower limitfis likewismmade and if this '4 test shows that there is an error, readjustment of the eccentric pin is made following which the test for the upper limit must be again made in order to insure that the readjustment has not so altered the gear tooth relationship as to insert a new error into the measurement at the upper limit. This however, is readily done since it requires, as has been stated, no disassembling or reassembling of the gage structure.

While I have described a preferred embodiment of my invention, it is to be understood that this description-is for purposes of illustration only and no limitation is to be implied other than that of the appended claims.

"Whatis claimed is:

1. In agear driven dial indicator of the shockpr'oof type having a measuring plunger, a rack slidable thereon, an indicating pointer and a gear train interconnecting the rack and pointer, means for adjusting the relationship of said rack to said plunger and thereby adjusting the relationship of said rgears'or said-gearitra'in to each other :to remove the-ieifects of defects in the gear teeth, said means comprisingan eccentric pin in said rack, said pin cooperating withrsaid plunger to determineithe relationship :therebetween.

2. Ina gear driven dia1 indicator of'the shockproof type having ameasuring plunger with an abutment thereonga rack slidable thereon, an

indicating pointer and a gear train interconnecting the .irack and the pointer and in which the position r the ia'k is determined Joythe position of the abutment on the -plunger, means for adjusting the position o'fthe rack with respect to the plunger, said'means womprising an eccentric pin 'rotatahly mounted in the "rack and "havingits eccentric portion cooperating with the abutment on the plunger, whereby-rotation of the said eccentric *pinwillalter flae position and relationship of the -rack Withm'espedt to the "plunger and therebyiietermine the teeth o'f the gear train which are "incenta'ct over the useful range of measurement of the indicator and eliminate erroneous Teadingsresulting from slight de- "fects in the'gear tooth-contours.

ALFRED H'Amn'reN EMERY.

anrnanwons UIKIED Thefolloiwing re'fererilces are of (record .in the file of this patent:

UNITED STATES PATENTS 'Ostberg ...Dec. '1, 1942 

